Previously, when you have sent Pokémon into battle, there has only been one possible entrance animation, the one for Shiny Pokémon. In Diamond, Pearl, Platinum, HeartGold and SoulSilver, these could be edited by using various Seals, but that didn't carry over to Generation V. However, Pokémon Black 2 & White 2 have added two further animations, and Omega Ruby & Alpha Sapphire added one more

Shiny Pokémon

Manually Addable?: No

Method:
The Shiny Pokémon are the more common entrance animation. When you encounter and send out a Shiny Pokémon, you will notice that it is of a different colour. In addition to this, a circle of sparkles will go around the Pokémon to indicate that it is shiny.

Method:
In Black 2 & White 2, you will be able to find a few rare Pokémon dotted around the areas of Unova. When you capture these Pokémon, you will learn that they were once under the control of the trainer N. Upon entry in battle, they have a special sound and are surrounding by a ring of green/yellow diamonds. Unfortunately, N's Pokémon can't be shiny.

Method:
In Black 2 & White 2, there is one final animation added. If you use your Pokémon within the PokéStar movies and deviate from the script, while still accomplishing the mission, your Pokémon will become a star and will be given this animation. Upon entry of battle, a star will shoot up from the Pokémon and bounce back down.

Method:
In Omega Ruby & Alpha Sapphire, a brand new entry animation was added. This animation is added to Pokémon if they have won the Master Rank Contests in every category: Beautiful, Coolness, Cuteness, Cleverness and Toughness. This is also denoted by the Contest Star Ribbon. Upon entry into battle, the Pokémon will sparkle for a little and have a red ribbon hover over it while the overworld goes briefly darker.